Heretofore, a pilot-controlled switching valve assembly has been known which comprises a main valve and a pilot valve for opening and closing the main valve, and various types of pilot-controlled switching valve assemblies have been proposed.
Fundamentally, all types of pilot-controlled switching valve are provided with (1) a manual operation member, such as a button, (2) a pilot valve movable in conjunction with the manual operation member, (3) a main valve and a pressure chamber disposed on the side of a back surface of the main valve, and designed to open the main valve in response to releasing a primary pressure in the pressure chamber by use of the pilot valve.
A specific structure of the conventional pilot-controlled switching valve assembly will be described below.
FIG. 19 is a schematic diagram showing one example of the conventional pilot-controlled switching valve assembly, which is disclosed in Japanese Patent Laid Open Publication No. 09-060969 (Patent Publication 1).
As shown in FIG. 19, this type of pilot-controlled switching valve assembly comprises a manual operation member 100 to be pressed by a push button or the like, a push rod 102 having a base end connected integrally or directly to the manual operation member, a pilot valve 104 provided at a distal end of the push rod 102, a diaphragm main valve 108 having a pilot-valve port 106 designed such that the pilot valve 104 is selectively brought into contact therewith and separated therefrom, a housing 112 defining a pressure chamber 110 formed on the side of the back surface of the main valve 110, and a valve seat 114 designed such that a front surface of the main valve 110 is selectively seated thereon and unseated therefrom. The pilot-controlled switching valve assembly also includes a sealing member 116 disposed at a portion of the housing 112 allowing the push rod 102 to penetrate therethrough, and a small hole 118 formed in a peripheral portion of the main valve 108.
FIG. 20 is a schematic diagram showing another example of the conventional pilot-controlled switching valve assembly, which is disclosed in Japanese Patent Laid Open Publication Nos. 11-304245 (Patent Publication 2) and 2001-098596 (Patent Publication 3).
As shown in FIG. 20, this type of pilot-controlled switching valve assembly has the same fundamental structure as that of the type illustrated in FIG. 19, and additionally includes a buffer mechanism (coil spring) 120 interposed between the manual operation member 100 and the base end of the push rod 102.
Patent Publication 1: Japanese Patent Laid Open Publication No. 09-060969
Patent Publication 2: Japanese Patent Laid Open Publication No. 11-304245
Patent Publication 3: Japanese Patent Laid Open Publication No. 2001-098596
The aforementioned conventional pilot-controlled switching valve assembly illustrated in FIG. 19 is designed such that the pilot valve 104 disposed within the pressure chamber 110 is brought in contact with and separated from the pilot-valve port 106 of the main valve 108, so that the pilot valve 104 is opened and closed to switch between water-stop and water-discharge states.
Thus, in an operation for switching from the water-discharge state to the water-stop state, it is firstly required that the pilot valve 104 be pressed through the push rod 102 in a direction allowing the pilot valve 104 to be brought into contact with the pilot-valve port 106. During this process, while the push rod 102 and the pilot valve 104 receive an upward force from a water pressure in the pressure chamber 110 and thereby the manual operation member 100 has to be pressed against the upward force, this required force is a very small value.
Then, when the pilot valve 104 is brought into contact with the pilot-valve port 106 of the main valve 108, a water pressure is acting on the main valve 108 in a direction allowing the main valve 108 to be moved away from the valve seat 114, and thereby the water-stopping operation has to be performed by use of a sufficient force against this water pressure. During this process, while the main valve 108 is moved toward the valve seat 114, this movement is performed at a low speed, which means that the pilot valve 104 forcibly presses the main valve 108 toward the valve seat 114. This forcible pressing of the main valve 108 toward the valve seat 114 causes the occurrence of water hammer when the main valve 108 is brought into contact with the valve seat 114, which leads to deterioration in operational feeling.
During the water-stopping operation, the conventional valve assembly illustrated in FIG. 19 has the difference (unevenness) in operational force between (1) before the pilot valve 104 is brought into contact with the pilot-valve port 106 and (2) after the pilot valve 104 is brought into contact with the pilot-valve port 106, resulting in undesirable operational feeling.
The pilot-controlled switching valve assembly illustrated in FIG. 20 is provided with the buffer mechanism 120 interposed between the manual operation member 100 and the base end of the pilot valve 104 to absorb a moving distance (displacement) of the pilot valve 104 in its stroke direction so as to provide improved operational feeling.
However, in this type of pilot-controlled switching valve assembly, a spring load onto the buffer mechanism 118 cannot be set at a low value, and thereby a spring constant of the buffer mechanism 118 cannot be set at a small value. Thus, the addition of the buffer mechanism 118 cannot contribute to improvement in operational feeling.
Specifically, when the pilot valve 104 disposed within the pressure chamber 110 is externally operated, the bottom surface of the pilot valve 104 is subjected to a water pressure for an area equivalent to the cross-sectional area of the push rod 102, and this water pressure acts on the push rod 102 (pilot valve 104) to move it away from the pilot-valve port 106. Therefore, a spring load on the buffer mechanism 120 has to be set at a value equal to or greater than the water pressure (if this is not done, the pilot valve 104 cannot be brought into contact with the pilot-valve port 106).
Consequently, it is difficult to downsize the buffer mechanism 120 in the conventional valve assembly illustrated in FIG. 20. Moreover, during the water-stopping operation, this type of conventional valve assembly still has the difference (unevenness) in operational force between (1) before the pilot valve 104 is brought into contact with the pilot-valve port 106 and (2) after the pilot valve 104 is brought into contact with the pilot-valve port 106, resulting in an undesirable operational feeling.
When a mixing faucet using a push button is developed, it is required to employ a pilot-controlled switching valve assembly as described above, but the conventional pilot-controlled switching valve assemblies involve the above problems. Thus, there is a need to be solve these problems.